The present invention relates to semiconductor packages and the method for manufacturing the same and, more particularly, to a semiconductor package having a semiconductor chip and bonding wire exposed to a core-hollowed portion on said encapsulation body.
With the development of electronic products, semiconductor packages are rapidly developed with the trends of manufacturing electronic devices of high performance and miniaturization. Therefore, surface built-in semiconductor packages such as QFP (Quad Flat Package), BGA (Ball Grid Array), TSOP (Thin Small Outline Package) and image sensor devices are widely used for the resin encapsulated semiconductor packages.
Structures of the aforesaid image sensing device is to mount an image-sensor semiconductor chip inside an encapsulation body having a core-hollowed portion. Then, after performing wire bonding to the chip, hermetically seal a transparent lid over the opening of the core-hollowed portion of the encapsulation body. In the configuration of an image-sensor chip package, however, there was involved such a problem that because flashes of the resin are formed on the surface of the lead frame during the molding process, the resulting quality of the die attachment and wire bonding on the flashed parts of the lead frame are found to become bad. In order to solve the foregoing problem, many ways for de-flashing are disclosed, for example, U.S. Pat. No. 5,070,041 disclosed a semiconductor packaging method by removing resin flash built up on lead frame without damaging resin molded section.
This patented method comprises the steps of: (1) coating an layer of high molecular organic substance over the areas of the lead frame that are uncovered by the encapsulation body wherein the high molecular organic substance has a melting point higher than the molding temperature of a resin constituting the encapsulation body; (2) injecting the resin into the mold and obtaining a core-hollowed portion of encapsulation body integrated with the lead frame; (3) using a special solvent to wash away the high-molecule organic coating, whereby the resin flash can be removed together with the high-molecule organic coating; (4) mounting semiconductor chip onto the flash-free die pad and wire-bonding electrodes of the semiconductor chip to the lead frames; (5) hermetically sealing a transparent lid to the opening of the core-hollowed portion of the encapsulation body.
The above-mentioned patented method is preferred than other prior art designs, bit it still has the following drawbacks. First, the solvent for removing the high molecular organic substances would cause pollution to the environment. Improper post-treatment of the solvent would raise environmental issue and thus, the cost is increased. Further, the step of coating high-molecule organic substance and the subsequent step of dissolving the coating to remove resin flash are quite complicated in procedure and costly to implement, therefore making the overall fabrication process quite cost-ineffective. Moreover, it is required to implement new facility and procedure than prior art to effectively remove the solvent containing high molecular organic substances, and therefore increase the cost of the overall fabrication process. In addition, after the organic high indecular substances dissolved in the solvent, the die-bonding and wire-bonding processes are not allowed to perform until the solvent being removed, which increases the fabrication time and reduces the production rate.
Accordingly, an object of the present invention is to provide an encapsulated semiconductor divice having a flash-proof structure and a manufacturing method thereof, by which resin flash formed on a lead frame is prevented during the molding process and therefore provide higher reliability of the semiconductor packaging device and the manufacturing cost is low so as to assure the quality in the package.
To achieve the aforesaid object, the present invention provides a process for producing an encapsulated semiconductor device having a flash-proof body, the process comprising the steps of: providing a lead frame with a flash-proof body on the lead frame so that a top of the lead frame in the flash-proof body is isolated from the other portion of the lead frame out of the flash-proof body; further, a die bonding area is formed on a portion at the top surface of the lead frame within the flash-proof portion and a wire bonding section at an outer side of the die bonding area; positioning the lead frame integrated in the flash-proof body within a mold and filling resin into the mold, thereby obtaining an encapsulation body having a core-hollowed portion integrated with part of the lead frame so that the encapsulation body encapsulates part of the lead frame are exposed within the core-hollowed portion of the encapsulation body; die-bonding a semiconductor chip to the top surface of the die pad on the lead frame; wire bonding to electrically connect the semiconductor chip to the wire bonding area on the lead frame; and attaching a lid to the encapsulation body to hermetically seal the whole core-hollowed portion of the encapsulation body.
In one preferred embodiment, the flash-proof body is constituted by a dam bar and a tape adhered to the dam bar. The dam bar is formed on an top surface of the lead frame while the tape is adhered onto the bottom surface of the lead frame. And further, the dam bar is adhered to the lead frame and the tape. The dam bar is protruded from a top surface of the lead frame with a proper height and is tightly adhered to the tape at the bottom surface thereof so that the top surface of the lead frame enclosed by the dam bar (i.e., die bonding area and wire bonding area) is completely isolated from the other part of the lead frame out of the dam bar and the tape. Therefore, in the molding process, the edge of the core-hollowed forming block of the encapsulation body used in the molding process will press hardly against the dam bar on the lead frame, thereby an enhanced contact between the dam bar and core-hollowed forming block is achieved. The foregoing arrangement can prevent the melted resin flowing into the die bonding area and the wire bonding area on the laed frame, and can prevent the formation of the resin flash occurred thereof.
In another preferred embodiment of the present invention, a groove portion formed by conventional etching techniques is positioned in a manner underlying the location of the dam bar on the lead of the lead frame. The groove portion according to the present inventin is used to limit the formation range of the dam bar on the lead and further to enhance the adherence between the dam bar and the lead on the lead frame.
In the present invention, the lead frame is constituted by a die pad and a plurality of leads. A gap is formed on the lead frame to allow the inner portion of the leads to be seperated from the tip portion of the die pad in a predetermined distance. Accordingly, a tape is attached and thus cover onto the bottom surface of the die pad and the bottom surface of the leads respectively, allowing the bottom side of the gap to be tightly sealed by the tape. A dam bar formed on the inner portion of the leads thereof is tightly sealed with each of the lead on the lead frame and with the tape underlying the leads respectively. The wire bonding area is positioned in a section of the lead frame between the inner portion of the leads and the dam bar. The die bonding area is positioned in the top surface of the die pad. The lead frame can be constituted only by a plurality of leads. The inner portion of the lead is seperated with a proper distance so as to be formed as a hollow portion. Therefore, after the semiconductor chip is attached to the die pad, the hollow portion is exactly inserted by the semiconductor chip for avoiding the delamination of the chip because of increasing the adhesive area between chip and lead frame. Now, the tape is adhered to the bottom surface of the lead frame with an area larger than the area of the hollow portion and the semiconductor chip. Therefore, after the dam bar is formed on a predetermined position of the lead frame, the wire bonding area of each lead frame for wire-bonding is enclosed inside the dam bar. In other words, in the lead frame formed by only leads, the die bonding area and the wire bonding area are positioned on a portion in which the leads concentrates towards the inner portion.